Ashley Olsen, artist found dead in apartment in Florence, Italy on 9 January 2016Instagram

The Senegalese immigrant suspected of being the killer of 35-year-old American artist Ashley Olsen in Florence has been identified. Italian police arrested Cheikh Tidiane Diaw on Wednesday (13 January) at his home, chief prosecutor Giuseppe Creazzo announced during a news conference.

"We have collected very serious evidence of his guilt," Creazzo said, Reuters reported. Investigators linked Diaw to the murder scene after discovering DNA evidence in a condom and on a cigarette in Olsen's flat, where Diaw's fingerprints were also found. Creazzo said that Diaw had taken his victim's mobile phone, put his SIM card in it and was using it when he was arrested.

According to CNN, police believe the two met at a Montecarlo nightclub and went to Olsen's flat together, where they had consensual sex under the influence of alcohol and possibly drugs. Olsen was then strangled by something "other than bare hands" and also suffered two fractures to her cranium. Authorities are waiting for the results of toxicology tests.

"We think sexual relations occurred before the homicide, not during it," Creazzo said, according to MailOnline. "We do not know whether they took drugs together before she was killed but we are awaiting the results of the analysis."

Creazzo said that during a long interrogation that concluded at 4am local time, Diaw had "substantially admitted" to the prosecutors's reconstruction of events leading up to Olsen's death. Italian media reported that Diaw allegedly told police he did not mean to kill Olsen but that she had fallen during an argument.

Diaw allegedly admitted: "She told me to leave and that her boyfriend was coming and she pushed me to the door." He then said he punched her in the head, screaming: "You have treated me like a dog." According to MailOnline, Olsen fell back, got up and attempted to push him away. He then shoved her, leading her to fall and hit her head.

"It is likely that the killer and victim were not lucid at the time of the murder," Creazzo added. "We have reason to believe that they took substances that made them not lucid. Alcohol for sure, maybe other substances. We will know more when the drugs tests on Ashley come back."

Olsen, who is originally from Summer Haven, Florida, was discovered by her boyfriend, Italian-American artist Federico Fiorentini, on 9 January after he had not heard from her for days following a spat. Fiorentini convinced Olsen's landlady Claudia Colivicchi to open the apartment for him. The two discovered Olsen on a bed with bruises and scratches on her neck.

Police said Fiorentini, who attempted to revive Olsen with CPR when he found her, has an alibi and is not considered a suspect in the case. Olsen's body was identified by her father, Walter Olsen, who teaches at Bianca Cappello Art Academy in the city. Diaw remains in police custody and is charged with murder, aggravated by cruelty.